1. Field of the Invention
The present invention relates to magnetic disk drives. The invention relates to a magnetic actuator lock which does not require the use of separate permanent magnets or electromagnets but uses the drive's own voice coil motor magnets to provide attracting forces. The invention also combines advantageous features in a very small form factor made possible by a novel mechanical and electronics design.
2. Related Art
A disadvantageous feature of disk drives that is well known in the art today is the problem of head/disk `crashes`. In fact, the word `crash`, although generally used, is somewhat misleading, in that read/write heads rarely crash on to the disk surface during normal operation of the drive when the head is flying in a stable mode. The problem refers more often to the after-effects of the head sitting on the disk surface after the drive has been powered down. The vast majority of known disk drives operate in the mode where the head takes off and lands on the disk, usually in a so-called `parking and landing` zone. Depending on surface characteristics of the disk and head, the head may adhere to the disk and fail to take off correctly (stiction problem), or the surface of the head may become contaminated by material (e.g. lubricant) from the disk causing the head to fly at an unstable altitude, thus degrading performance and perhaps leading to a catastrophic failure.
Prevention of this `crash` or `stiction` phenomenon depends largely on strict control of the disk surface quality and of the chemistry, consistency and deposition of surface lubricant. This is difficult and expensive process for the typical disk drive, and failure to maintain standards can have repercussions at a later date. However, even if the surface quality is maintained, problems may still arise between head and disk as a result of rough handling, during movement of the drive after power down. Rough handling may cause damage to the head, disk or both. In this the latter case, the impact may be minimized if the heads have been parked in the parking zone, where no customer data is written. Generally, current disk drives either implement a park command or can sense that a power down is occurring and automatically move the heads to the parking zone.
Another approach, known in the art, to solving these head disk problems is to design the drive in such a way that the heads are physically removed from the disk surfaces at switch-off or by specific command. This has generally been done by moving the heads both vertically away from the surfaces and laterally away from the edge of the disks. This technique was a necessary and common practice in the earlier days of the disk drive industry, when disk cartridges were much in use, and before the development of the modern lightly-loaded head and lubricated disk. Again however, the techniques used for this technique are complicated, difficult to set up and normally make use of solenoids and lifting devices. U.S. Pat. No. 4,661,873 shows such a device. It involves many separate elements, such as springs, pins, arms, solenoid, magnetic shields, etc.
For all the above reasons, it is desirable to provide a disk actuator parking system which removes the heads from the disk surfaces, either on command or at power-off, with minimum complexity and number of components.
A further disadvantageous feature of disk drives at the present time is the method used to lock the actuator, which supports the read/write heads, whether in the landing zone or on a head ramp.
Generally known methods used to lock the actuator in either the landing zone or on the ramp can be broadly classified into two groups. The first group consists of methods that use electromagnetic solenoids to move a locking pin, arm or other feature which mechanically prevents the actuator from moving once power is applied to the solenoid. This method has numerous disadvantages, including the power consumption required to keep the solenoid energized while the drive is operating. This method also adds considerable cost to the disk drive because of the solenoid itself as well as the electronic circuits required to operate the solenoid.
A second widely known method used to latch the actuator in the correct position typically employs a permanent magnet and a magnetically permeable material such as steel to hold the actuator in position by magnetic attraction. This method has the disadvantage that it requires a separate permanent magnet to provide the attractive force in addition to the permanent magnets commonly used for the voice coil motor. This increases the drive cost and complexity.
Therefore, it is desirable to provide a method for locking the actuator in the correct zone which does not require the use of an electromagnetic solenoid or a separate permanent magnet.
The features of low acoustic noise, damping and simplicity of head parking are especially desirable in disk drives subject to portable applications. Portability itself has its own requirements and objectives. In the computer world, specific designs for portability began in the early 1980's with personal computers weighing around 30 lbs. and supplied with carrying handles. These were more accurately described as `luggable` rather than `transportable`. This style of portable computer has since evolved into second generation `laptop` machines, weighing and measuring considerably less. In parallel with these size-reduction trends in the computer world, the rigid disk drive industry has witnessed its own miniaturization over the last twenty years, from approximate disk diameters of 28" in the 1960's, to 14" and 8" in the 1970's, to 5.25" and 3.5" in the 1980's. These trends in disk drive form factors have been matched by complementary improvements in data storage densities, performance, power requirements and price. The increasing sophistication, availability and universality of popular software during the last few years has fueled the requirement for versatile, high-performance personal computers and driven the hardware developments in the industry. Taking all of those trends together, the growing demand for laptop computers requires a matching availability of small, light-weight, high-performance hard disk drives with data storage capability equivalent to that obtained on drives designed for desktop computers.
There is a demand, therefore, for a small disk drive with typically 40 Megabyte storage capacity suitable for use in very small computer systems, such as laptops, or other systems requiring off-line memory, and with the associated features of quietness, ruggedness and high performance.